Glass mat with reinforcing binder

ABSTRACT

In gypsum board faced with a fibrous mat, for example, a mat of glass filaments adhesively bound together, improvements are realized by the use of a reinforcing resinous binder in the mat.

FIELD OF THE INVENTION

This invention relates to an improved fibrous mat of the type that canbe used as a facing material for gypsum board.

Panels of gypsum wallboard having a core of set gypsum sandwichedbetween two sheets of facing paper have long been used as structuralmembers in the fabrication of buildings where the panels are used toform the partitions or walls of rooms, elevator shafts, stair wells,ceilings and the like. Although paper sheets have long been used as thefacing material for gypsum board, there are prior art disclosures whichsuggest the use of other kinds of facing materials for gypsum board. Forexample, Canadian Pat. No. 993,779 and U.S. Pat. No. 3,993,822 disclosegypsum boards having facing sheets of glass fibers. More particularly,the Canadian patent discloses gypsum board comprising a set gypsum coresandwiched between two glass fibermats which are porous anddimensionally stable in the presence of moisture. The mats are adheredto the core by portions of the set gypsum which comprises the core. Itis believed that the developments described in the aforementionedpatents were never commercialized.

A more recent development in the field of gypsum board is the subject ofU.S. Pat. No. 4,647,496 to C. W. Lehnert and B. G. Randall, assigned tothe same assignee as the present invention. This patent disclosesimproved forms of fibrous mat-faced gypsum board which have beencommercialized and which are presently being used effectively in moreand more applications. These include applications in which paper-facedgypsum board is considered unsuitable for use and certain applicationswhere it has been recognized that the fibrous mat-faced gypsum board canbe used to better advantage than paper-faced board.

A preferred form of the gypsum board described in the aforementioned'496 patent includes board faced with a glass mat comprising fiber glassfilaments oriented in random pattern and bound together with anadhesive, for example, a resin binder, with the outer face of each ofthe glass mats being substantially free of set gypsum. Another preferredform of the gypsum board described in the '496 patent is one in whichthe set gypsum core of the board includes a water-resistant additive,for example, wax-asphalt emulsion, preferably in admixture withpoly(vinyl alcohol).

In general, fibrous mat-faced board of the type described above hascertain characteristics which are considered more desirable than thoseof paper-faced gypsum board. For example, the surface of fibrousmat-faced gypsum board is water-resistant whereas conventional papercover sheets used to face gypsum board tend to soak up water and todelaminate upon becoming wet. Accordingly, the fibrous mat-faced boardhas much better weathering characteristics in outdoor applications thanpaper-faced gypsum board, particularly those forms of board whichinclude a water-resistant additive in the gypsum core of the board.Unlike a paper cover sheet, a fibrous mat does not expand or contractduring the manufacture of the board; this reduces cockle and permits themanufacture of board with uniform dimensions. These are but a few of theadvantages of fibrous mat-faced board relative to conventionalpaper-faced board. New advantages are being realized as use of thefibrous mat-faced board is expanded into other applications.

A proposed use for fibrous mat-faced gypsum board is as a support memberin a roofing application of the type known commonly as a"built-up-roof," often referred to as "BUR". A built-up-roof is amulti-ply structure which is formed in place and which comprisesalternate layers of a hydrocarbon water-proofing material such asasphalt or tar and of sheets of roofing material such as sheets of feltor fiberglass, for example, two or three plies of each of theaforementioned. A BUR is typically topped off with stone or pebbles thatadhere to the hydrocarbon water-proofing material. By way of example, aBUR can be fabricated by pouring hot asphalt onto a support member andapplying to the hot liquid asphalt a layer of roofing felt in the formof sheets. This sequence of steps is repeated until the roof is built upto the desired extent and then stones or pebbles are added to the toplayer of asphalt to which they adhere.

It is known to use as the support member onto which the first layer ofhot liquid asphalt or similar material is poured a wood fiber, perlite,or paper-faced gypsum board. It has been recognized that fibrousmat-faced board has inherent characteristics that would seemingly makeit more suitable for use as the support member in a BUR than heretoforeused materials. However, it has been found that pouring hot asphalt ontothe surface of a fibrous mat-faced gypsum board results in the formationin the asphalt of voids which remain in the solid asphalt layer which isformed upon cooling. (A similar phenomenon has been observed in the useof paper-faced gypsum board as a support member in a BUR.) It appearsthat the hot asphalt, which typically has a temperature of 400° to 450°F. or higher, causes residual water in the gypsum board to vaporize. Thevaporized water penetrates through the facing material and into the hotasphalt where it tends to form blisters or bubbles which can burst. Thisleads to a defective ply in the built-up-roof.

One aspect of the present invention relates to the provision of afibrous mat-faced gypsum board that can be used effectively as a supportmember in a built-up-roof.

There are other problems associated with fibrous mat-faced gypsum board,and they are problems that are more pronounced when the fibrous matcomprises glass fibers particularly glass fibers in non-woven form. Forexample, the glass fibers can cause itching or other mild irritation ofthe skin as the board is handled. Also, glass fibers can becomedislodged from the mat, become airborne, and function as an irritant.

Another shortcoming of glass is that it tends to be degraded by alkalinematerials. This restricts the use of glass mat-faced gypsum board inapplications where, for example, an alkaline-based adhesive is appliedto the glass mat for the purpose of adhering thereto an overlyingmaterial such as panels of insulation.

Other aspects of the present invention relate to the provision of animproved glass mat which has a reduced tendency to cause irritation tothe skin and which has improved resistance to being degraded by alkalinematerials.

SUMMARY OF THE INVENTION

In accordance with one aspect of this invention, there is provided afibrous mat having a predetermined thickness and comprising fibers boundtogether with an adhesive and including also a reinforcing resinousbinder on the surface of the mat and extending but partway through thethickness of the mat into the interstices thereof, the amount ofreinforcing resinous binder being about 3 to about 40 g/square meter ofmat.

An important aspect of the present invention is that the improvedproperties of the mat of the present invention can be achieved by theuse of very small amounts of the reinforcing resinous binder, forexample, preferred amounts being about 5 to about 15 g of resin/squaremeter of mat.

In accordance with another aspect of this invention, there is providedgypsum board comprising a set gypsum core having adhered to at least oneof its surfaces a nonwoven glass fiber mat having a predeterminedthickness and comprising glass fibers bound together by an adhesive andincluding also a reinforcing resinous binder on the surface of the matand extending but partway through the thickness of the mat into theinterstices thereof, the amount of the binder being such that the dryingcharacteristics of the board are substantially the same as boardcomprising said mat without said binder An important aspect of thisembodiment of the invention is that it is possible to manufacture gypsumboard provided with the improved mat of the present invention on anindustrial manufacturing line without having to adopt inefficientprocedures for the purpose of accomodating the drying of the board, forexample, raising oven temperatures and/or increasing oven size and/orslowing down the line speed of the manufacturing operation so that theboard has a longer residence time in the oven. (It is noted that theindustrial manufacture of gypsum board entails forming and shaping anaqueous gypsum slurry into a panel-like shape, maintaining such shape asthe calcined gypsum sets and then accelerating the drying of theresulting board by subjecting it to elevated temperatures.) The use ofan amount of reinforcing binder which significantly deters theevaporation of water from the wet gypsum core through the mat wouldrequire the use Of higher temperatures and/or longer residence times inorder to maintain line speed or the use of slower line speeds whilemaintaining standard temperatures and residence times. Remarkably, ithas been found that the improved properties which are possessed by boardof the present invention can be achieved by use of amounts of areinforcing resinous binder which do not significantly change the dryingcharacteristics of the board.

In preferred form, the mat comprises continuous or discrete strands orfibers of glass in non-woven form which are bonded together by aresinous adhesive and the reinforcing resinous binder of the mat isalkaline-resistant.

In preferred form, the improved mat of the present invention is formedin situ during the manufacture of fibrous mat-faced gypsum board.Accordingly, another aspect of the present invention encompasses aprocess for manufacturing in continuous fashion a fibrous mat-facedgypsum board comprising:

(A) forming an aqueous slurry of calcined gypsum;

(B) continuously feeding said aqueous slurry onto an underlying, movingand supported facing sheet;

(C) forming said deposited slurry as it is carried on said moving sheetinto a panel-like shape and maintaining said panel-like shape while saidcalcined gypsum sets to form a wet board;

(D) applying to the top surface of said panel-like shape of slurry anoverlying porous fibrous mat of predetermined thickness and comprisingfibers bound together by an adhesive;

(E) allowing said slurry to penetrate but partway into the thickness ofsaid overlying mat so that the outer surface of said mat issubstantially free of set gypsum;

(F) applying to the outer surface of said mat a reinforcing resinousbinder which penetrates but partway into the thickness of said mat, theamount of binder so applied being such that the drying characteristicsof the board are substantially the same as board comprising said matwithout said binder; and

(G) drying the wet board, thereby forming board comprising a set gypsumcore having adhered to one surface thereof said facing sheet and to theother surface thereof said mat.

In carrying out the process of the present invention, there is provideda gypsum board comprising a set gypsum core having at least one of itssurfaces faced with an improved fibrous mat of the present invention,the mat being adhered to the core by set gypsum of the core whichpenetrates but partway through the thickness of the mat.

The present invention offers a number of advantages. For example, thereinforcing resinous binder, notwithstanding its being used in suchsmall amounts, is effective in deterring the formation of voids in alayer of material formed by applying to the surface of the fibrousmat-faced gypsum board a water-proofing material in hot liquid form.This permits the gypsum board of the present invention to be usedeffectively as a support member in a built-up-roof. In addition, glassmat which includes the reinforcing resinous binder tends to cause lessirritation to skin and the reinforcing resinous binder functions to keepthe fibers from being dislodged readily from the mat. Another importantadvantage of the present invention is that presently-used industriallines for manufacturing fibrous mat-faced gypsum board can be adaptedreadily with equipment for forming the improved mat of the presentinvention.

Other attributes of the present invention will become apparent from thefollowing detailed description.

DETAILED DESCRIPTION OF THE INVENTION

The fibrous mat-faced gypsum board of the present invention comprises aset gypsum core which is basically the type of core used in those gypsumstructural products which are known as gypsum wallboard, dry wall,gypsum board, gypsum lath and gypsum sheathing. The core of such aproduct is formed by mixing water with powdered anhydrous calciumsulfate or calcium sulfate hemihydrate (CaCO₄.1/2H₂ O) known as calcinedgypsum, and thereafter allowing the mixture to hydrate or set intocalcium sulfate dihydrate (CaSO₄.2H₂ O), a relatively hard material. Thecore of the product will in general comprise at least about 85 wt.percent of set gypsum.

The composition from which the set gypsum core is made can includeoptional constituents, including, for example, those includedconventionally in fire-resistant gypsum board and in water-resistantgypsum board. Examples of such constituents include set accelerators,retarders, foaming agents, dispersing agents, water-resistant additivesand fire-resistant additives.

For use as a support member for a built-up-roof, the core of the fibrousmat-faced gypsum board should include a water-resistant additive,preferably in an amount such that the core absorbs no more than about10% and preferably no more than about 5% water when tested in accordancewith ASTM method C-473 with only the edges exposed. Any suitablewater-resistant additive can be used. Numerous examples of suchadditives are disclosed in the aforementioned '496 patent. A preferredmaterial for use in improving the water-resistant properties of thegypsum core comprises wax-asphalt emulsion, species of which areavailable commercially, as described also in the '496 patent. The amountof wax-asphalt emulsion used can be within the range of about 3 to about10 wt. %, preferably about 5 to 7 wt. %. A particularly preferredmaterial for use in improving the water-resistant properties of thegypsum core comprises a mixture of materials, namely, poly(vinylalcohol) and wax-asphalt emulsion of the aforementioned type, asdescribed in said '496 patent. The amounts of poly(vinyl alcohol) andwax-asphalt emulsion used should be at least about 0.05 wt. % and about2 wt. % respectively. The preferred amounts of poly(vinyl alcohol) andwax-asphalt emulsion are about 0.15 to about 0.4 wt. % and about 3 toabout 5 wt. % respectively. (Unless stated otherwise, the term "wt. %"when used herein means weight percent based on the total weight of theingredients of the composition from which the set gypsum core is made,said ingredients including the water of the wax-asphalt emulsion, butnot including additional amounts of water that are added to the gypsumcomposition for forming an aqueous slurry thereof.) A highly preferredwater-resistant additive for use in the core of the gypsum-based boardis an organopolysiloxane, for example, of the type referred to in U.S.Pat. Nos. 3,455,710; 3,623,895; 4,136,687; 4,447,498; and 4,643,771.Within this class of materials, poly(methyl-hydrogen-siloxane) isparticularly preferred. The amount of the organopolysiloxane should beat least about 0.2 wt. %. A preferred amount falls within the range ofabout 0.3 to about 0.6 wt. %.

The improved fibrous mat of the present invention comprises a materialwhich is capable of forming a strong bond with the set gypsum comprisingthe core of the gypsum board of the present invention. As disclosed inthe aforementioned '496 patent, examples of such materials include amineral type material such as glass fibers and synthetic resin fibers.The mat of the present invention is in non-woven form and includesfibers which are bound together by an adhesive and includes also areinforcing resinous binder. The mat of the present invention is porousand can be made by treating a non-woven mat made up of adhesively-boundfibers with the reinforcing resinous binder. As described in detailbelow, the mat of the present invention is formed preferably during themanufacture of the fibrous mat-faced gypsum board.

In preferred form, the non-woven mat which is treated with thereinforcing resinous binder pursuant to the present invention is a glassmat comprising continuous or discrete strands of glass fibers adhesivelybonded together, preferably by a resinous material. The mat can range inthickness, for example, from about 15 to about 40 mils, with a thicknessof about 25 to about 35 mils being preferred. Such mats are known andare commercially available in many forms. In highly preferred form, themat is a fiber glass mat comprising fiber glass filaments oriented inrandom pattern and bound together with a resin binder. Fiber glass matsof this type are commercially available for example, those sold underthe trademark DURA-GLASS by Manville Building Materials Corporation andthose sold by ELK Corporation as BUR or shingle mat.

The reinforcing resinous binder that is applied to the aforementionedfibrous mat can be any polymeric material that is capable of adheringstrongly to the mat, and is preferably a material that is considered bythe art to be water-resistant and heat-resistant and, most preferably,alkaline-resistant also. It is desirable also that the resin haveanti-blocking characteristics. There are many commercially-availableresins that possess the aforementioned characteristics. The binder cancomprise a single resin or a mixture of resins and can be athermoplastic or a thermoset resin. For most applications, the binder islikely to be a resin which is different from the adhesive which holdstogether the fibers of the mat. However, the same resin can be used forthe reinforcing binder and for the adhesive.

The reinforcing resinous binder is preferably applied to the fibrous matin the form of an aqueous dispersion of resin solids, that is, a latex.Because of the relatively small amount of resin used to treat the mat,it is recommended that a commercially-available latex be diluted priorto applying the latex to the mat. Good results have been achieved withlatexes that have been diluted to the extent that the solids contentsthereof are about 5 to about 25 wt. %.

The fibrous mat is most desirably treated with substantially 100% of theresin. However, it should be understood that other materials which arecompatible with the resin and which do not interfere with thecoalescence of the resin particles or desired properties of the mat canbe used also. Examples of such materials include pigments, lubricants,and fillers such as silicates, silica, gypsum and calcium carbonate. Theamount of such other materials can comprise up to about 75 wt. % of acomposition comprising the resin and other materials. However, when suchother materials are used, it is preferred that they comprise not morethan about 25 wt.% of the composition.

A preferred reinforcing resin binder for use in the practice of thepresent invention is available in the form of a latex sold by UnocalChemicals Division of Unocal Corporation under the mark76 RES 1018. ThepH and solids content of the latex are, respectively, 7.5-9.0 and 50%.The resin is styrene-acrylic copolymer which has a relatively lowfilm-forming temperature (20° C.) and a Tg of 22° C. Coatings formedfrom the resin can be dried effectively at temperatures within theranges of about 300° to 400° F. If desired, a coalescing agent can beused to lower the film-forming temperature.

Another preferred reinforcing resin binder for use in the practice ofthe present invention is also available in the form of a latex sold byUnocal Chemicals Division of Unocal Corporation. This preferred latex issold under the mark 76 RES 2302. The pH and solids content of the latexare, respectively, 3.5 and 45%. The resin is a self-crosslinking vinylacetate-acrylic copolymer which has a Tg of about 33° C.

As mentioned above, the amount of reinforcing resin binder applied tothe surface of the fibrous mat is relatively small, for example, sosmall that to the naked eye it is difficult, if not impossible, todetect differences between the untreated and the binder-treated mat.Nevertheless, the use of such small amount of binder is effective inimparting desired properties to the mat, as described above. The reasonsfor this are not understood. Particularly perplexing is determining thereason why such small amounts of binder are effective in inhibiting theformation of bubbles and/or voids in a layer of hydrocarbonwater-proofing material that is formed by the solidification of thematerial in hot liquid form on the surface of the treated fibrousmat-faced board.

The minimum amount of reinforcing resinous binder to apply to thefibrous mat is that which results in detectable improvements in thedesired properties of the mat. In quantitative terms, it is recommendedthat the binder be applied in an amount of at least about 3, andpreferably at least about 5, g/square meter of mat. Several factors canbe taken into consideration in determining the maximum amount of binderto use. As mentioned above, manufacturing considerations dictate thatthe binder should be present in an amount such that the dryingcharacteristics of the board are not changed substantially. In additionthese should be avoided amounts which tend to interfere withcharacteristics of the substantially gypsum-free surface of the mat thatare considered desirable for particular applications. Suchcharacteristics include both aesthetic and functional characteristics.In connection with functional characteristics, it is noted that a matwhich is substantially free of set gypsum is highly textured andprovides an excellent substrate for adhering thereto an overlyingcomponent inasmuch as it comprises many interstices into which anadhesive composition can flow and bind. Amounts of reinforcing resinousbinder which would eliminate this characteristic should be avoided.Other factors which influence the maximum amount of reinforcing resinousbinder that is used include a levelling off of or elimination ofimprovements in properties notwithstanding the use of increased amountsof the binder. Amounts of binder which cause blocking should be avoidedalso. It is believed that for most applications, it will not benecessary to apply more than about 25 g of resin per square meter ofmat, but higher amounts can be used, as mentioned above. A preferredamount of binder to use with the preferred glass mat of the presentinvention is about 5 to about 15 g/square meter of mat, withparticularly good results being achieved with the use of about 10 toabout 15 g/square meter of mat.

The reinforcing resinous binder can be applied to the mat by anysuitable means, for example, spray, brush, curtain coating, and rollercoating. The means used to apply the binder will generally depend on theform of the binder, for example, whether it is in solid or liquid form(dissolved, dispersed or suspended). Spray has been used veryeffectively when applying the binder in the form of a latex.

As mentioned above, an important feature of the present invention isthat the improved fibrous mat-faced gypsum board can be made utilizingan existing, but readily-modified manufacturing line for applying thereinforcing resinous binder to the surface of the mat. In conventionalfashion, dry ingredients from which the gypsum core is formed arepre-mixed and then fed to a mixer of the type commonly referred to as apin mixer. Water and other liquid constituents used in making the coreare metered into the pin mixer where they are combined with the dryingredients to form an aqueous gypsum slurry. Foam is generally added tothe slurry in the pin mixer to control the density of the resultingcore. The slurry is dispersed through one or more outlets at the bottomof the mixer onto a moving sheet which is indefinite in length and isfed from a roll thereof. The sheet forms one of the facing sheets of theboard. In preferred form, the sheet is a fibrous mat like that which isapplied subsequently to the top of the slurry.

As is common practice in the manufacture of conventional paper-facedgypsum board, the two opposite edge portions of the sheet areprogressively flexed upwardly from the mean plane thereof and thenturned inwardly at the margins as to provide coverings for the edges ofthe resulting board.

A sheet of fibrous mat to which the reinforcing resinous binder is to beapplied is fed from a roll onto the top of the slurry, therebysandwiching the slurry between the two moving sheets which form thefacings of the set gypsum core which is formed from the slurry.Conventional shaping rolls and edge guiding devices are used to shapeand maintain the edges of the composite until the gypsum has setsufficiently to retain its shape.

In preferred form, the reinforcing resinous binder in the form of adiluted latex is applied uniformly to the surface of the fibrous mat bya multiplicity of spray heads which are positioned over the mat andacross the width thereof. The surface of the mat to which the binder isapplied is substantially free of set gypsum and comprises manyinterstices into which the binder can flow and bond. The formation ofthe board with the facing mat being substantially free of gypsum can beaccomplished by known means, for example, by adjusting the viscosity ofthe gypsum slurry so that it penetrates but partway into the overlyingfibrous mat, for example, up to about 30 to 70% of its thickness overthe entire surface areas thereof.

It is believed that, for many applications, it will be most advantageousto manufacture board having both surfaces faced with a fibrous mat, witheach mat having a substantially gypsum-free surface. The recommendedknown means for controlling the viscosity of the slurry is to addthereto a viscosity-control agent. Such viscosity-control agents areknown in the field of gypsum board manufacture. A preferredviscosity-control agent is paper fiber. Examples of other agents thatcan be used are cellulosic thickeners, bentonite clays and starches. Theparticular viscosity values that are used in manufacturing operation canvary from one application to the next, depending on the porosity of themat, and the desired penetration of the slurry. Accordingly, for anyparticular application, the viscosity value is best determinedempirically.

In using the preferred form of glass fiber mat, as described above, tomanufacture the aforementioned preferred forms of board, it isrecommended that the gypsum slurry have a viscosity within the range ofabout 5000 to about 7000 cp. As used herein, the viscosity value refersto Brookfield viscosity measured at a temperature of 70° F. at 10 rpmutilizing paddle No. 3. It should be appreciated that the amount ofviscosity-control agent added to the slurry to give the desiredviscosity will vary depending on the particular agent used and thespecific viscosity desired.

The reinforcing resinous binder can be applied at that stage of themanufacturing process at which the gypsum has set partially and to theextent that it is in a non-flowable form. Preferably, the binder isapplied to the surface of the mat when the gypsum has set completely butat a time prior to the drying of the board. Typically, the binder willbe present in those portions of the mat that are not occupied by setgypsum, with the highest concentration of binder being at the surface ofthe mat.

After application of the binder, sequential lengths of the board are cutand further processed by exposure to heat which accelerates the dryingof the board by increasing the rate of evaporation of excess water inthe gypsum slurry and water of the latex.

As mentioned above, the amount of the reinforcing resinous binder can besuch that the drying characteristics of the board are substantially thesame as board faced with mat that does not include the binder. (It isbelieved that the porosity characteristics of the mat are notsignificantly changed.) This means that industrial drying conditionstypically used in continuous gypsum board manufacture can be used in themanufacture of board of the present invention. Exemplary dryingconditions include temperatures of about 200° to about 600° F., dryingtimes of about 30 to about 60 minutes, and line speeds of about 70 toabout 250'/minute.

It is believed that the form of the board that will be used most widelyis board that has but one of its fibrous facings treated with thereinforcing resinous binder. However, both fibrous facings of the boardcan include the binder in accordance with the present invention. One wayof making such board is to first apply the binder to one of the fibrousfacings in the manner described above and thereafter applying binder tothe other facing after the board has been dried.

Thus, improved gypsum board can be provided by use of a mat having apredetermined thickness and comprising fibers and resinous adhesivematerial which holds the fibers together, the amount of adhesivematerial being substantially the same throughout a first portion of themat which extends from one surface thereof to about 30% to about 70% ofthe thickness thereof and the amount of adhesive material being greaterin a second portion of the mat comprising the remaining mat thickness,the amount of the adhesive material in said second portion varying, withthe highest proportion thereof being present at the other surface of themat. The aforementioned amounts are on the basis of amount of resin perunit volume of mat.

Examples which follow are illustrative of the present invention.

EXAMPLES

This example is illustrative of a fibrous mat-faced gypsum board whichhas a water-resistant core and which can be used as a support member ina built-up-roofing structure in accordance with the present invention.

The formulation set forth below is an example of an aqueous gypsumslurry which can be used in making the core of a gypsum board faced withan improved fibrous mat of the present invention.

    ______________________________________                                        Constituents       Lbs./1000 sq. ft. of Board                                 ______________________________________                                        calcined gypsum    1380                                                       CaSO.1/2  H.sub.2 O)                                                          wax/asphalt emulsion,                                                                            130                                                        water-resistant additive                                                      aqueous solution of 10 wt. %                                                                     56                                                         poly(vinyl alcohol), water-                                                   resistant additive                                                            paper fiber        15                                                         set accelerator    6                                                          ammonium lauryl sulfonate                                                                        l                                                          foaming agent                                                                 calcium lignosulfonate,                                                                          2                                                          dispersing agent                                                              water              1,000                                                      ______________________________________                                    

The wax/asphalt emulsion of the above formulation contains approximately48 wt. % solids of which about 11 wt. % is paraffin wax and about 37 wt.% is asphalt. The set accelerator comprises about 80 wt. % potash, about12 wt. % lignosulfonate and about 8 wt. % ground gypsum.

The above formulation is used to prepare gypsum board, the surfaces ofwhich are covered with non-woven fiber glass mat. The mat is composed ofglass fiber filaments oriented in a random pattern bonded together by anadhesive referred to by the manufacturer as a "modifiedurea-formaldehyde resin". The mat has a thickness of 33 mils and is moreporous than paper of the type used as the cover sheet of gypsumwallboard. The air permeability of the mat is 700 CFM/sq.ft. (testmethod FG 436-910). The mat is available commercially as DURA-GLASS7502-2 lbs. and is an example of a preferred glass mat for use in thepractice of the present invention.

Continuous length board is made from the above gypsum slurry and glassfiber mat on a conventional wallboard machine. The viscosity of thegypsum slurry and the porosity of the glass fiber mat are such that thesurfaces of both glass fiber mats which form the facings of the boardare substantially free of set gypsum, with portions of set gypsum of thecore penetrating about 50% of the thickness of the overlying mat.

Prior to the cutting and the drying of the board and when the gypsum hasset completely, there is sprayed onto the surface of the overlying glassmat an aqueous dispersion of UNOCAL 76 RES 2302 latex that is dilutedwith water from its normal 45% solids content to 10% solids. The aqueousdispersion of resin is sprayed onto the surface of the mat at 40lbs./sq. inch pressure and at a rate of 0.4 gallon/minute as theconveyor belt carrying the gypsum board travels at a speed of 85ft./min. Four 95°-angle spray tips are used to apply the resindispersion uniformly to the glass mat, depositing thereon about 2.2 lbs.of resin per 1000 sq.ft. of mat (about 11 g of resin per square meter ofmat). The resin penetrates about 50% of the thickness of the mat.

After application of the resin dispersion the board is cut into 8 ft.lengths and thereafter the board segments are placed in an oven having atemperature of about 400° F. for about 30 mins. and until the board isalmost dry, and then at 200° F. for about 15 mins. until it is driedcompletely. The density of the board is about 48 lbs./cu.ft.

For the purpose of evaluation, the dried board is rubbed by hand. Thefibers of the treated mat are more resistant to removal than the fibersof untreated mat.

There is applied to the surface of the treated glass mat hot liquidasphalt having a temperature of about 400° F. The asphalt is allowed tocool and solidify into a solid film having a thickness of about 3/16inch. The film is continuous and has no bubbles or voids. The sameprocedure is followed except that hot liquid asphalt is poured onto thesurface of an untreated mat. The solifified film has blisters and voidsin it over about 40% of its surface.

In another evaluation, contact adhesive is applied to the surfaces ofboth treated and untreated glass mat facings of gypsum boards. Theuntreated mat soaks up the contact adhesive quickly. In contrast, thecontact adhesive placed on the mat treated with the reinforcing resinousbinder remains on the surface to a much greater extent. This isadvantageous in that lower amounts of adhesive can be used and bondstrength to overlying materials is improved.

Tensile strength tests have been conducted on gypsum board faced with aglass mat formed from glass fibers having a diameter of 16 microns. Thetests included evaluation of untreated glass mat and glass mat treatedwith a reinforcing resinous binder (the resin of the aforementioned 76RES 2302 latex) in an amount of about 11 g/square meter. Specimens ofexpanded polystyrene foam were adhered to the surfaces of the untreatedand treated mats by a water-based acrylic adhesive. The bond between thefoam and treated mat was about 25% stronger than the bond between thefoam and the untreated mat.

In summary, it can be said that the present invention provides a unique,practical, and economical way to improve the properties of fibrousmat-faced gypsum board and to overcome or mitigate problems associatedwith the fibrous facing thereof, particularly glass type facing of thenon-woven type. The reinforcing resinous binder functions to help keepintact fibers that otherwise tend to become air-borne as the board ishandled and installed by the hammering of nails or with a screw gun. Itfunctions also to protect the skin from being irritated by glass fiberswhich can be abrasive. It makes it possible to use such boardeffectively in built-up-roofing applications and it provides an improvedsurface for adhering thereto overlying structural elements.

I claim:
 1. A fibrous mat having a predetermined thickness and propertyand comprising fibers bound together with and adhesive and includingalso a reinforcing resinous binder on the surface of the mat andextending but partway through the thickness of the mat into theinterstices thereof, so that said mat porosity is not significantlychanged, the amount of reinforcing resinous binder being about 3 toabout 40 g/square meter of mat.
 2. A mat according to claim 1 whereinthe amount of binder is no greater than about 25 g/square meter of mat.3. A mat according to claim 1 wherein the amount of binder is about 5 toabout 15 g/square meter of mat.
 4. Gypsum board comprising a set gypsumcore having at least one of its surfaces faced with a fibrous mataccording to claim 1, the mat being adhered to the core by set gypsum ofthe core which penetrates but partway through the thickness of the mat.5. Gypsum board comprising a set gypsum core having adhered to at leastone of its surfaces a non-woven glass fiber mat having a predeterminedthickness and porosity and comprising glass fibers bound together by anadhesive and including also a reinforcing resinous binder on the surfaceof the mat and extending but partway through the thickness of the matinto the interstices thereof, so that said predetermined mat porosity isnot significantly changed, the amount of the binder being such that thedrying characteristics of the board are substantially the same as boardcomprising said mat without said binder.
 6. Gypsum, board according toclaim 5 wherein the amount of binder is at Least about 3 g/square meterof mat.
 7. Gypsum board according to claim 6 wherein the amount ofbinder is about 5 to about 15 g/square meter of mat.
 8. Gypsum boardaccording to claim 4, 5, 6, or 7 wherein aid mat comprises fiber glassfilaments oriented in random pattern and bound together with a resinbinder.
 9. Gypsum board according to claim 8 wherein said reinforcingresinous binder is a styrene-acrylic copolymer.
 10. Gypsum boardaccording to claim 8 wherein said reinforcing resinous binder is aself-crosslinking vinyl acetate-acrylic copolymer.
 11. A built-up-roofincluding a support member comprising the gypsum board of claim 4 or 5and adhered thereto a continuous film of hydrocarbon water-proofingmaterial formed by the solidification of a hot liquid form of thematerial.